Threshold driven dynamic comparator

Abstract

In one embodiment, a method receives an analog input voltage. The method also receives a threshold from a plurality of thresholds. A comparator performs a comparison of the input voltage with the received threshold and outputs an output value based on the comparison of the analog input voltage with the received threshold. The output value is for converting the analog input voltage to a digital value. The method determines if the threshold should be adjusted based on the comparison and adjusts the threshold when it is determined the threshold should be adjusted.

1. A method comprising:
 receiving an analog input voltage; 
 receiving a threshold from a plurality of thresholds; 
 performing, at a comparator, a comparison of the analog input voltage with the received threshold; 
 outputting a comparison decision based on the comparison of the analog input voltage with the received threshold; 
 determining if the threshold should be adjusted based on the comparison; 
 adjusting the threshold when it is determined the threshold should be adjusted; 
 determining a time during a sample phase; 
 freezing the threshold when the time is determined such that the threshold is not adjusted again until the sample phase ends, wherein before the time, the threshold was adjustable; 
 determining a last comparison decision for the sample phase after the freezing of the threshold; and 
 outputting an output value for the sample phase based on comparison decisions determined during the sample phase, wherein the output value is for converting the analog input voltage to a digital value. 
 
     
     
       2. The method of  claim 1 , wherein the threshold is not adjusted if the time period has elapsed even if the analog input voltage has passed the threshold. 
     
     
       3. The method of  claim 1 , further comprising:
 determining a plurality of comparison decisions based on comparisons of the analog input voltage with thresholds in the plurality of thresholds, 
 wherein the output value is based on the plurality of comparison decisions. 
 
     
     
       4. The method of  claim 3 , wherein a comparison decision in the plurality of comparison decisions is based on a threshold in the plurality of thresholds not being used in the comparisons. 
     
     
       5. The method of  claim 1 , wherein the plurality of comparison decisions correspond to a plurality of bits in the digital value. 
     
     
       6. The method of  claim 1 , wherein adjusting the threshold comprises adjusting the threshold to a threshold selected from the plurality of thresholds if the analog input voltage has passed the threshold. 
     
     
       7. The method of  claim 6 , wherein determining if the threshold should be adjusted comprises:
 receiving the comparison decision from the comparator; and 
 determining the threshold should be adjusted if the analog input voltage has passed the threshold based on the output value. 
 
     
     
       8. An apparatus comprising:
 a multiplexer configured to output a threshold from a plurality of threshold values; 
 a comparator configured to: 
 receive an analog input voltage; 
 receive the threshold from the multiplexer; 
 perform a comparison of the analog input voltage with the received threshold; and 
 output a comparison decision based on the comparison of the analog input voltage with the received threshold, 
 circuitry configured to: 
 determine if the threshold should be adjusted based on the comparison; 
 cause the multiplexer to adjust the threshold when it is determined the threshold should be adjusted; 
 determine a time during a sample phase; 
 freeze the threshold when the time is determined such that the threshold is not adjusted again until the sample phase ends, wherein before the time, the threshold was adjustable; 
 determine a last comparison decision for the sample phase after the freezing of the threshold; and 
 output an output value for the sample phase based on comparison decisions determined during the sample phase, wherein the output value is for converting the analog input voltage to a digital value. 
 
     
     
       9. The apparatus of  claim 8 , wherein the circuitry is configured to output a selection signal to the multiplexer to cause the multiplexer to output a threshold selected from the plurality of thresholds. 
     
     
       10. The apparatus of  claim 9 , wherein the circuitry is configured to:
 determine when the time in the sample phase is determined; and 
 not output the selection signal thereby freezing the threshold such that the threshold is not adjusted again until the sample phase ends. 
 
     
     
       11. The apparatus of  claim 9 , wherein the circuitry is configured to:
 receive the comparison decision for the threshold from the comparator; 
 determine if the comparison decision indicates the analog input voltage has passed the threshold; 
 output the selection signal to the multiplexer to cause the multiplexer to adjust the threshold if the analog input voltage has passed the threshold; and 
 not output the selection signal to the multiplexer if the analog input voltage has not passed the threshold. 
 
     
     
       12. The apparatus of  claim 8 , wherein the multiplexer comprises a plurality of inputs for the plurality of thresholds. 
     
     
       13. The apparatus of  claim 8 , wherein the plurality of thresholds comprise different portions of a reference value. 
     
     
       14. The apparatus of  claim 13 , wherein the different portions of the reference value are used to determine a bit in the digital value. 
     
     
       15. The apparatus of  claim 8 , wherein the comparator is configured to:
 determine a plurality of comparison decisions based on comparisons of the analog input voltage with thresholds in the plurality of thresholds, 
 wherein the output value is based on the plurality of comparison decisions. 
 
     
     
       16. The apparatus of  claim 15 , wherein a comparison decision in the plurality of comparison decisions for the output value is determined when the threshold has been passed by the analog input voltage. 
     
     
       17. The apparatus of  claim 15 , wherein a comparison decision in the plurality of comparison decisions is based on a threshold in the plurality of thresholds not being used in the comparisons by the comparator. 
     
     
       18. An analog to digital converter comprising the apparatus of  claim 8 , wherein the apparatus is a stage in the analog to digital converter.